A known guide bar includes guide plates in the region of its tip on each longitudinal side thereof. The guide plates project laterally beyond the guide paths of the guide groove. The radial projection is provided in such a manner that the chain links are laterally substantially covered and only the cutting links extend beyond the edge of the guide plates. In this way, it is ensured that for plunge cutting, the depth of penetration of the cutting teeth into the wood to be cut is reduced. Difficulties with respect to the manipulation during plunge cutting work are intended to be reduced thereby.
A too large a projection of the side walls, however, negatively affects the cutting power and plunge cutting work during tree maintenance is thereby hampered. On the other hand, if the projection of the side walls, especially in the direction-changing region of the guide bar, is too low, then the manipulation of the motor-driven chain saw is made more difficult.
It is an object of the invention to provide a guide bar wherein the guidance of the saw chain is improved while retaining good cutting power during plunge cutting work and to provide a guide bar which can be used for saw chains of different configurations.
The guide bar of the invention is for guiding the saw chain of a motor-driven chain saw. The saw chain includes center drive links, cutting links and connecting links pivotally interconnected with bolts or rivets. The drive links include respective rakers and the guide bar includes: an elongated flat base body having mutually adjacent guide surfaces along the periphery thereof for supporting said connecting links and said cutting links as the saw chain is moved about said guide bar during the operation of the chain saw; said mutually adjacent guide surfaces being separated by a guide groove for receiving said rakers therein; said base body having a front end; a direction-changing front end assembly arranged on said front end of said base body for said saw chain; and, said front end assembly including: a rotatably mounted idler sprocket for engaging and guiding said saw chain about the front end of said guide bar; guide discs attached to said idler sprocket at respective sides thereof so as to rotate therewith; said guide discs having a number of radially projecting sections; and, said idler sprocket having a number of teeth equal to the number of sections of each of said guide discs.
The idler sprocket is held in the direction-changing section of the guide bar and the guide plates are configured as rotating discs in the direction-changing section. The rotating discs are connected to the idler sprocket so as to rotate therewith. With this configuration, the advantages of a reliable guidance of the motor-driven chain saw with the aid of guide plates on the guide bar are combined with a good cutting power. In lieu of circularly-shaped edges in the region of each tooth of the idler sprocket, the guide discs have radially projecting sections. These sections can have a rectangular shape, a rhombic shape or a trapezoidal shape.
The dimensioning of the guide discs is adapted to the dimensions of the guide bar and the idler sprocket so that the width of the gaps or cutouts between the radially projecting sections of the guide discs in the peripheral direction of the guide discs is approximately as large as the length of the roof sections of the cutting links. The cutting links include a side or lateral cutting edge which has a contour laterally offset outwardly referred to the running direction of the saw chain and projects beyond the side surfaces of the guide disc in the region of the cutout. The radial outer edge of the guide discs ends at a slight distance just below the roof cutting edge so that the tip of the cutting roof section of the cutting tooth of a cutting link projects beyond the axial edge of the guide disc. The cutouts between the radially projecting sections of the guide disc are preferably longer than the width of the radially projecting sections in the peripheral direction.
The edges of the radially projecting sections which extend in the radial direction of the guide discs can be configured as cutting edges in order to support the lateral cutting work. Preferably, the edges run in a radial direction inclined in opposition to the rotational direction of the guide discs. Each radially projecting section and each roof section follow one behind the other in this way during operation of the motor-driven chain saw. The depth limiter of a cutting link advantageously comes to rest in the region of the leading edge of a radially projecting section viewed in the rotating direction of the guide discs. At the direction-changing section, the idler sprocket is surrounded at both sides by side plates which axially guide the idler sprocket and project radially therebeyond. Respective bearings for rotatively journaling the idler sprocket and the disc are provided in the side plates. The guide discs are preferably connected to the idler sprocket so as to rotate therewith and are driven by the moving saw chain. The guide discs are exchangeably mounted at the direction-changing section of the guide bar and can be exchanged with the saw chain. It can be practical to so configure the guide bar that the guide discs can be turned over in that the guide discs are essentially configured to be axial symmetrical with respect to their basic outline. Preferably, the guide discs are provided with a largest possible number of radially projecting sections.